We report 2 cases of Haemophilus parainfluenzae endocarditis and review 34 cases of HACEK endocarditis from the literature. HACEK organisms are the most common cause of Gram-negative endocarditis in children. They have a propensity to form friable vegetations (especially H. parainfluenzae) that break off and cause symptomatic emboli. HACEK endocarditis (from a review of the 36 published cases) may involve previously normal hearts (33%), may be complicated by embolization (31%) and may require vegetectomy or other surgery (31%). Mortality with HACEK endocarditis was 14%. HACEK organisms may be resistant to penicillins but are susceptible to third generation cephalosporins.